The invention is directed to a method of managing the braking force applied on the wheels of a vehicle, wherein the brake actuators comprise a pneumatic actuator and an electric actuator. In particular, safety functions, such as ABS and ESP are performed using hybrid actuators activated by both electrical energy and pneumatic energy.
The braking system of the vehicles, designed to brake the vehicle under request of the driver, comprises in addition automatic safety functions, such as an antilock brake system (ABS), an electronic stability control (ESC), or a traction control system (TCS). In case of a pneumatic brake, the air pressure applied to the brakes is electronically managed, in such a way that the vehicle is braked under safe conditions. The safety functions are performed by the means of complicated and expensive electro-pneumatic systems and valves. Further, in case of failure within the pneumatic circuit, the safety functions may be disabled.
In the framework of weight reduction, and reduction of the energy consumption of the vehicles, hybrid brake actuators are used, which are activated by both pneumatic energy and electric energy. Example of such a hybrid brake actuator is described in the patent application PCT/EP2014/001813. However, the safety functions above-mentioned are still performed by the pneumatic system, and thus present the same drawbacks than a traditional pneumatic braking system.
It is desirable to improve the safety functions of a braking system comprising hybrid brake actuators.
The present invention provides a method of managing the braking force on a wheel of a vehicle equipped with at least a pair of hybrid brake actuators, wherein each hybrid brake actuator comprises a pneumatic brake actuator, delivering a main braking force, and an electric brake actuator, delivering a complementary braking force. The present method comprises the steps of:
Determining a targeted braking force,
Applying a main braking force to the wheel by the means of a first actuator;
applying a complementary braking force to the wheel by the means of a second actuator in such a way that the requested braking force is effectively delivered;
Monitoring the braking force delivered at the wheel,
modulating one or more of the main braking force and the complementary braking force,
The main braking force and the complementary braking force are preferably applied in such a way that the main braking force is equal or higher than the complementary braking force. The resulting delivered braking force may be limited to the maximal braking force of the pneumatic system in order to avoid overstress of the braking system.
In one aspect, the complementary braking force is modulated at each individual wheel to provide the safety functions like ESC, ABS or TCS. To this extend, the complementary braking force may be automatically released or increased depending on the running conditions.
In another aspect, the main braking force is equally modulated at two or more wheels to provide the safety functions, like ESC, ABS or TCS, and the complementary braking force is in turn modulated at each individual wheel.
The main braking force and the complementary braking force are preferably managed by two separate ECUs.
In a further aspect, the complementary braking force allows to compensate potential failure of the safety functions in the pneumatic system.
In particular, the method may further comprise the steps of
Monitoring one or more of the main braking force and the global braking force applied to the wheel,
Identifying a failure within the pneumatic system,
Deactivating one or more of the pneumatic safety functions,
Activating or over activating the electrical actuator to provide one or more of the safety functions.
In addition, the present method allows to compensate braking failure of the pneumatic system, in case air pressure is not sufficient to reach the targeted braking request, by activation or over activation of the electrical brake actuators.
According to the present method, one or more of the pneumatic brake actuators and electrical brake actuators may also be automatically activated.
The present invention is further directed to a vehicle having at least a pair of hybrid brake actuators, comprising a pneumatic brake actuator and an electric brake actuator, and wherein the braking force is managed according to the method hereby described.